1. Field of the Invention
The present invention generally relates to a method for depositing aluminum on a permanent Nd—Fe—B magnet.
2. Description of the Prior Art
Because permanent Nd—Fe—B magnets contain large amounts of rare earth elements, the permanent Nd—Fe—B magnets can be easily oxidized when it is exposed to air or under a damp environment. Accordingly, the magnetic properties of the permanent Nd—Fe—B magnets are reduced and, therefore, cannot function properly. In order to prevent oxidation, many manufacturers have deposited an anti-corrosive layer on the surface of the permanent Nd—Fe—B magnets. Because aluminum has a greater anti-corrosion property, there has been a constant development in the aluminum plating technologies. Currently, one of the existing aluminum plating technologies is vacuum deposition. Vacuum deposition of aluminum provides for a film of aluminum on the permanent Nd—Fe—B magnets that has a smooth surface; however, the film of aluminum has poor adhesion to the permanent Nd—Fe—B magnets. Another one of the existing aluminum plating technologies is a combination of multi-arc magnetron sputtering. Although multi-arc ion plating causes large particles of aluminum to be formed on the surface of the permanent Nd—Fe—B magnet, magnetron sputtering are used to patch the surface of the permanent Nd—Fe—B magnet to provide a smooth surface; however the efficiency of the depositing the film of aluminum on the permanent Nd—Fe—B magnet is low.
Through researching the multi-arc ion plating process, it was found that large particle of aluminum formation is caused by the low melting point of aluminum and the high temperature of the ion arc in the multi-arc ion plating process. As a result, the anti-corrosion properties for the film of aluminum are negatively affected. Although magnetron sputtering is used to patch the surface of the permanent Nd—Fe—B magnet to provide a smooth finish, the efficiency of the depositing the film of aluminum on the permanent Nd—Fe—B magnet is low. Typically, it takes approximately 5 hours to deposit the film of aluminum on the permanent Nd—Fe—B magnet.
Such a method is disclosed in Chinese Patent Publication CN101736304A. The method includes a first step of removing grease and dust from a permanent Nd—Fe—B magnet to produce a purified permanent Nd—Fe—B magnet. The next step of the method is disposing the purified permanent Nd—Fe—B magnet in a chamber of a multi-arc ion plating apparatus. After disposing the purified permanent Nd—Fe—B magnet in the chamber, air is removed from the chamber of the multi-arc ion plating apparatus to lower pressure in the chamber of the multi-arc ion plating apparatus to a first reduced pressure. Next, an electric potential is applied to the purified permanent Nd—Fe—B magnet in the chamber of the multi-arc ion plating apparatus to clean the purified permanent Nd—Fe—B magnet. A film of aluminum is then disposed on the purified permanent Nd—Fe—B magnet using an arc source to produce a coated permanent Nd—Fe—B magnet.